1. Field of the Invention
This invention relates to a thermal transfer sheet which comprises a substrate film and a release layer, a protective layer, and a hot-melt ink layer provided in that order on the substrate film, has excellent thermal transferability, and can provide a thermally transferred print having excellent scratch resistance and heat resistance.
2. Background Art
Various thermal transfer sheets are known in the art, and, in particular, among them are a thermal dye transfer sheet comprising a substrate film bearing a dye layer containing a thermally sublimable dye and a binder and a hot-melt thermal transfer recording sheet comprising a substrate film bearing a hot-melt ink layer containing a colorant, such as a pigment, and a vehicle, such as wax, are known in the art. According to a thermal transfer system using these thermal transfer sheets, various prints can be simply formed with a thermal head or the like. Therefore, in order to conduct the control of film products in factories and the like, the thermal transfer sheets in combination with the thermal transfer system have been used to print bar codes and the like on untreated PET labels and the like for product control purposes. For example, regarding a material and a layer construction for thermal transfer printing on a plastic film, a thermal transfer sheet comprising a substrate film bearing a thermal transfer layer formed of a resin having a softening temperature of 60 to 110.degree. C. and a colorant is known in the art (Japanese Patent Laid-Open No. 163044/1979).
However, when the conventional thermal transfer sheet is used to transfer a thermal transfer layer onto a smooth substrate film, such as an untreated PET film, the transfer per se is unsatisfactory and, at the same time, the transferred thermal transfer layer has poor scratch resistance and heat resistance, making it impossible to use the resultant print for the product control purposes in actual factories and the like. Therefore, the solution to the above problem and the development of a thermal transfer sheet, which has excellent thermal transferability and can provide a print having scratch resistance and heat resistance good enough to be usable for product control purposes in actual factories and the like, have been desired in the art.